All bulbous/tuberous plants benefit from allowing the foliage to yellow before severing the roots. Green foliage still manufactures food. Early interrruption of this process may sacrifice next year's bloom.

I would never let them go to seed but cut off the flower stem as the flower fades. Do you really have to dig and store glads in your area? Al

I am in the same zone, and never dig mine out (way too many bulbs). They come back year after year big and beautiful.
~Natalie

Yes, no need to to lift and store glad corms in the PNW - unless you do want to cull or replant in a different location. They are perfectly winter hardy in the ground here unless drainage is questionable.